On Fri, Feb 09, 2024 at 10:24:32AM -0800, Andres Freund wrote: > On 2024-01-26 07:42:33 +0100, Alvaro Herrera wrote: > > This suggests that finding a way to make the ifunc stuff work (with good > > performance) is critical to this work. > > Ifuncs are effectively implemented as a function call via a pointer, they're > not magic, unfortunately. The sole trick they provide is that you don't > manually have to use the function pointer.
The IFUNC creators introduced it so glibc could use arch-specific memcpy with the instruction sequence of a non-pointer, extern function call, not the instruction sequence of a function pointer call. I don't know why the upthread ifunc_test.patch benchmark found ifunc performing worse than function pointers. However, it would be odd if toolchains have replaced the original IFUNC with something equivalent to or slower than function pointers.
